Electronic Combination Lock Circuit

Description

This is the circuit diagram of a simple electronic combination lock using IC LS 7220.This circuit can be used to activate a relay for controlling (on & off) any device when a preset combination of 4 digits are pressed.The circuit can be operated from 5V to 12V.

To set the combination connect the appropriate switches to pin 3,4,5 and 6 of the IC through the header.As an example if S1 is connected to pin 3, S2 to pin 4 , S3 to pin 5, S4 to pin 6 of the IC ,the combination will be 1234.This way we can create any 4 digit combinations.Then connect the rest of the switches to pin 2 of IC.This will cause the IC to reset if any invalid key is pressed , and entire key code has to be re entered.

When the correct key combination is pressed the out put ( relay) will be activated for a preset time determined by the capacitor C1.Here it is set to be 6S.Increase C1 to increase on time.

For the key pad, arrange switches in a 3X4 matrix on a PCB.Write the digits on the keys using a marker.Instead of using numbers I wrote some symbols!.The bad guys will be more confused by this.

I had gone thru ur website and quiet interesting, U r proving the theory part of the electronics content where in we are into giving virtual lab. I am sure the synergy between will help the students/hobby users to learn your theory content and practice as well. Please let me know your good time to talk.

Hi Sundeep as per proelectron standards first digit stands for material. B stands for silicon and if it is A it is germanium. The second digit indicates the application C stands low power small signal low frequency transistor. 107 stands for the type number (may be voltage current etc)for details refer manufacturers catalog. the suffic A, B, C stands for small signal current gain of the transistor. A 100 t0 250, B 200 to 450, C 400 to 900.
The following do not fall on any standards.
SL 100 & CL100 S stands for the manufacturer Semiconductor India Ltd., C stands for Continental devices India Ltd. L100 stand for medium power NPN transistor. if it is K100 stands for medium power PNP transistor. BEL100N and BEL100P are also similar trasistors.

Currently I dont have a PCB lay out of this circuit.I tested this circuit on the bread board only.
You can easily make the PCB by yourself using software like PCB123.Just have a try.
If you cant make one properly, mail me. I will make one for you.